1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium, a magnetic recording medium and a magnetic recording and reproducing apparatus.
2. Description of the Related Art
A hard disk drive (HDD) that is a type of magnetic recording and reproducing apparatus has been currently increasing its recording density at an annual rate of 50% or more, and the recording density is said to be likely to continue to increase in the future. Following this, a magnetic head and a magnetic recording medium suitable for recording density growth have been developed.
In the magnetic recording and reproducing apparatus commercially available at present, a so-called perpendicular magnetic recording medium is mounted as a magnetic recording medium in which an easy axis of magnetization within a magnetic film is oriented mainly perpendicularly thereto. The perpendicular magnetic recording medium can prevent noise from increasing because the perpendicular magnetic recording medium is less subject to a diamagnetic field in a boundary region between recording bits in increasing the recording density and a clear bit boundary is formed. Moreover, the perpendicular magnetic recording medium has an excellent heat fluctuation property because a decrease in recording bit cubic volume associated with the recording density growth can be lessened.
Furthermore, in order to respond to the demand for further recording density growth of the magnetic recording medium, using a single magnetic pole head with an excellent ability to write to a perpendicular magnetic layer has been examined. More specifically, a magnetic recording medium has been proposed that improves efficiency of entrance and exit of a magnetic flux by providing a layer made of a soft magnetic material that is called a backing layer (or a protective layer) between the perpendicular magnetic layer of a recording layer and a non-magnetic layer.
In addition, in order to improve a record and reproduce characteristic of the perpendicular recording medium and the heat fluctuation property, a method is proposed in which a plurality of magnetic layers are formed by using an orientation control layer, and a crystal grain of each of the magnetic layers are made a continuous columnar crystal, thereby enhancing a perpendicular orientation characteristic, as disclosed in Japanese Laid-Open Patent Application Publication No. 2004-310910.
Moreover, Japanese Laid-Open Patent Application Publication No. 07-244831 discloses a method of preliminarily providing a crystalline orientation promoting layer on a substrate and depositing a perpendicular magnetic anisotropy thin film through the crystalline orientation promoting layer by sputtering at a sputtering gas pressure of 10 Pa or more.
Furthermore, Japanese Laid-Open Patent Application Publication No. 2007-272990 proposes using Ru as an orientation control layer. Ru is known to include a columnar crystal that includes a centroclinal protrusion formed on a top thereof. Because of this, by causing a crystal grain such as a magnetic layer on the protruding orientation control layer made of Ru to grow, by promoting a separate structure of the grown crystal grain, and by isolating the crystal grain, an effect of making the magnetic particle grow and form into a columnar shape can be obtained.
In addition, as disclosed in Japanese Laid-Open Patent Application Publication No. 2002-197630, a magnetic recording medium is known that includes a substrate, a ruthenium-containing layer deposited in a low pressure argon atmosphere (0.6 Pa) deposited thereon, a ruthenium-containing layer deposited in a high pressure argon atmosphere (10 Pa) deposited further thereon, and a perpendicular magnetic layer deposited on the top in sequence. By depositing the Ru layer under the high sputter pressure on the Ru layer deposited under the low sputter pressure, an orientation of the Ru layer can be improved, thereby improving the orientation of the perpendicular magnetic layer growing thereon and making the magnetic particle smaller.
Also, Japanese Laid-Open Patent Application Publication No. 2009-238299 discloses a method of reducing a size of a crystal grain of a Ru layer deposited under a high gas pressure by depositing the Ru layer under the high gas pressure on a Ru layer deposited under a low gas pressure and by causing the Ru layer deposited under the high gas pressure to contain Co and oxygen. Moreover, Japanese Laid-Open Patent Application Publication No. 2009-238299 illustrates B2O3 as an oxide contained in a granular layer.
However, in order to increase the recording density of the magnetic recording medium, there were problems described below, after performing a two-step film deposition by depositing a first Ru layer deposited by sputtering under a low pressure, and then depositing a second Ru layer deposited by sputtering under a high gas pressure on the first Ru layer, when depositing an orientation control layer including a minute crystal grain, and then reducing a size of a magnetic particle having a columnar structure of a perpendicular magnetic layer deposited on the orientation control layer.
More specifically, when sputtering under the high gas pressure, a mean free path of a sputter particle becomes short; energy is reduced; and gas molecules are likely to mix in a grown crystal, which reduce crystallinity and a film density of the deposited Ru layer. Accordingly, it was difficult to deposit a Ru layer having a high hardness by sputtering under the high pressure.
In order to deposit a Ru layer having a high hardness, it is thought not to use the sputtering under the high gas pressure. However, unless the sputtering under the high gas pressure is performed, the centroclinal protrusion becomes difficult to be formed on the top of the columnar crystal constituting the orientation control layer. Accordingly, it becomes difficult to obtain an effect of making the magnetic particle of the perpendicular magnetic layer smaller by separating the crystal grain of the perpendicular magnetic layer growing on the orientation control layer.
Due to this, conventionally, when depositing the orientation control layer by using the two step film deposition, in order to form the centroclinal protrusion on the top of the columnar crystal constituting the orientation control layer, the sputtering under the high gas pressure was performed at the cost of the hardness of the Ru layer. As a result, the magnetic recording medium including the orientation control layer deposited by using the two step film deposition was insufficient in the hardness of the surface thereof, and sufficient reliability cannot be obtained because the surface of the magnetic recording medium can be easily damaged.
Furthermore, a protruding shape caused by the centroclinal protrusion of the orientation control layer is transferred to the surface of the perpendicular magnetic layer, and then to a protective layer formed on a surface of the perpendicular magnetic layer. The Ru layer deposited by the sputtering under the high gas pressure has large irregularities in its surface. Hence, the magnetic recording medium including the orientation control layer including the Ru layer deposited by the sputtering under the high gas pressure has a high degree of roughness in its surface. When the degree of roughness of the surface of the magnetic recording medium is high, a floating height of a magnetic head becomes lower than ever, which becomes an obstacle to respond to the recording density growth.
As discussed above, in the conventional technique, there is a demand for providing a method for manufacturing a magnetic recording medium that can enhance the recording density by reducing the size of the magnetic particle having the columnar structure of the perpendicular magnetic layer, can have an excellent damage resistance in the surface thereof by depositing the orientation control layer having the high degree of hardness and the low surface roughness, can obtain the higher reliability, and can adjust to the further recording density growth.